/**
 * 
 * 求 1 + 2! + 3! + ... + 20! 的和。
*/
#if  1
#include <stdio.h>
int main()
{
    unsigned long long sum = 0;
    unsigned long long EachItem = 1;
    for (int i = 1; i < 21; i++)
    {
        /* code */
        EachItem = 1;
        for (int j = 1; j <= i; j++)
        {
            /* code */
            EachItem *= j;
        }
        
        sum += EachItem;
    }
    printf("%llu",sum);

    return 0;
}
#endif